The present invention relates to a method for manufacturing a magnetic head to be mounted on a VTR, etc., and a magnetic recording and reproducing apparatus.
FIG. 1 is a front view showing an example of a conventional magnetic head. The magnetic head shown in this figure includes a head base 1 and right and left chips 2 and 3 (which will be referred to as xe2x80x9cchip(s)xe2x80x9d hereinafter) that are adhered to the head base 1 via adhesives 4a and 4b. The chip 2 is formed by adhering metal plates (cores) 2a and the chip 3 is formed by adhering plates 3a, respectively. Around each of the metal plates 2a and 3a, a coil 5 is wound.
A gap 2b is a space at the adhering portion between the metal plates 2a of the chip 2, and a gap 3b is a space at the adhering portion between the metal plates 3a of the chip 3, respectively. Such a magnetic head is installed on a rotating cylinder (not shown in drawing) and slides on the magnetic tape.
FIG. 2 is an enlarged view showing the chip 2 of FIG. 1. GD 1 and GD 2 indicate the dimensions of the gap depth (depth of the gap), respectively. GD 1 indicates the dimension of the gap depth before grinding and GD 2 indicates the dimension of the gap depth after grinding. Furthermore, reference numeral 6 denotes a portion removed by grinding and the difference between GD 1 and GD 2 (GD 1xe2x88x92GD 2) is a grinding amount.
Such a grinding is carried out by installing the magnetic head on a rotation drum for grinding, and bringing a grinding tape 9 (see FIG. 1) into contact with the left and right chip fronts rotating integrally with a rotation drum.
FIG. 3 is a perspective view of the chip 2 seen from the upper side. Bo in this figure indicates the distance between the head gap 2c that is a gap at the front portion of the chip 2 and a top 7 of a curved surface of the chip front. A plurality of annular lines 8 indicate contour lines, where the lines closer to the inside means higher and the position at the top 7 means the highest. Since the contact condition of the magnetic tape becomes excellent at the top 7 portion, it is preferable that the top 7 is located as dose as possible to the head gap 2c. It is ideal that the top 7 is located on the head gap 2c, that is, Bo=0 is satisfied.
The measurement of the above-mentioned contour lines is carried out by measuring the top of the curved surface when the head gap 2c is seen from an extended part of the line extending between the head gap 2c and the rotation center of the rotation cylinder, with the use of an interference-pattern measuring device. For instance, when the diameter of the rotation cylinder is 21.7 mm, the measurement is carried out with the chip inclined by 3 degrees 10 minutes.
GD 2 and Bo are important factors affecting the performance of a magnetic head, and in the manufacturing process, it is necessary to screen a magnetic head having GD 2 and Bo ranging within the predetermined standard value satisfying the necessary performance. For instance, when the standard value of GD 2 is in the range from 10 to 15 xcexcm, a magnetic head with GD 1 of about 30 xcexcm was prepared and a magnetic head with GD 2 of the both chips after grinding in the range from 10 to 15 xcexcm and Bo in the range from xe2x88x9250 to 50 xcexcm was screened to be used.
Herein, in order to improve the transmission rate of the magnetic head, it is necessary not only to increase the number of magnetic heads to be mounted on one rotation cylinder but also to improve the head performance such as C/N (ratio of carrier wave output to noise) with respect to an individual magnetic head. It is known that when GD 2 is decreased, C/N is improved. Consequently, for improving the head performance, CD2 is preferably decreased.
However, in the above-mentioned conventional method for manufacturing a magnetic head having GD 1 of about 30 xcexcm, there was a problem in that variation in the difference between the both chips after grinding is large and the rate of GD 2 and Bo of the both chips being in the specified value is low, and thus the yield becomes low. It is thought that the same is true in the case of manufacturing the high performance magnetic head in which GD 2 is reduced as mentioned above. Therefore, in order to manufacture the high performance magnetic head efficiently, it was necessary to solve the problem with respect to the yield.
With the foregoing in mind, it is an object of the present invention is to provide a method for manufacturing a magnetic head with a high yield by setting the dimension of a gap depth of a head chip before grinding to be 25 xcexcm or less so as to reduce the defect in the dimension of the gap depth and the distance between the head gap and the top of the curved surface of the chip front, and to provide a magnetic recording and reproducing apparatus manufactured by this method.
In order to achieve the above-mentioned object, a method for manufacturing a magnetic head according to the present invention includes grinding a front of a head chip so as to form a front shape of the head chip, wherein the dimension of a gap depth of the head chip before grinding is 25 xcexcm or less. According to the above-mentioned method for manufacturing a magnetic head, it is possible to improve the yield of the magnetic head satisfying the standard values of both the dimension of the gap depth and the distance between the head gap and the top of the curved surface of the chip front. Therefore, it is possible to improve the productivity in manufacture of a high-performance magnetic head with a decreased gap depth.
In the above-mentioned method for manufacturing the magnetic head, it is preferable that the dimension of the gap depth before grinding is 20 xcexcm or less. Furthermore, in the method for manufacturing a magnetic head having the dimension of the gap depth before grinding of 20 xcexcm or less, it is preferable that the dimension of the gap depth after grinding is to be 1 xcexcm or more.
Furthermore, it is preferable that the dimension of the gap depth before grinding is 15 xcexcm or less. Furthermore, in the method for manufacturing the magnetic head having the gap depth before grinding of 15 xcexcm or less, it is preferable that the dimension of the gap depth after grinding is to be 1 xcexcm or more.
Furthermore, it is preferable that the difference between the dimension of the gap depth before grinding and the dimension of the gap depth after grinding is 19 xcexcm or less. According to the above-mentioned method for manufacturing a magnetic head, since the maximum value of the dimension of the gap depth before grinding is 25 xcexcm, by setting the grinding amount to be 19 xcexcm or less, it is possible to manufacture a magnetic head in which the magnetic head performance is improved while setting the standard value of the dimension of the gap depth to be 6 to 9 xcexcm. In this case, as compared with the conventional case of grinding the chip in which a dimension of the gap depth before grinding is about 30 xcexcm, the grinding amount becomes smaller. Thus, it is possible to improve the yield of the magnetic head satisfying the standard values of the dimension of the gap depth and the distance between the head gap and the chip front.
Furthermore, it is preferable that the difference between the dimension of the gap depth before grinding and the dimension of the gap depth after grinding is 14 xcexcm or less. According to the above-mentioned method for manufacturing the magnetic head, for example, when the dimension of the gap depth before grinding is set to 20 xcexcm or less, it is possible to manufacture a magnetic head in which the magnetic head performance is improved while setting the standard value of the dimension of the gap depth to 6 to 9 xcexcm. Also in this case, as compared with the conventional case, the grinding amount becomes smaller, and it is possible to improve the yield of the high-performance magnetic head.
Furthermore, it is preferable that the difference between the dimension of the gap depth before grinding and the dimension of the gap depth after grinding is 9 xcexcm or less. According to the above-mentioned method for manufacturing a magnetic head, for example, when the dimension of the gap depth before grinding is set to 15 xcexcm or less, it is possible to manufacture a magnetic head in which the magnetic head performance is improved while setting the standard value of the dimension of the gap depth to 6 to 9 xcexcm. Also in this case, as compared with the conventional case, the grinding amount becomes smaller, and it is possible to improve the yield of manufacturing the high-performance magnetic head.
Furthermore, it is preferable that a plurality of head chips are mounted on one magnetic head and the grinding is carried out with respect to the plurality of head chips simultaneously. According to the above-mentioned method for manufacturing a magnetic head, it is possible to reduce the difference in the dimension of the gap depth between a plurality of head chips, and variation in the difference of the distance between the head gap and the top of the curved surface of the chip front, thus improving the yield of a high performance magnetic head.
Next, a magnetic recording and reproducing apparatus of the present invention includes a magnetic head manufactured by the above-mentioned method for manufacturing a magnetic head to be mounted. According to the above-mentioned magnetic recording and reproducing apparatus, since the magnetic head manufactured by the manufacturing method of the present invention is used, the magnetic recording and reproducing apparatus can be manufactured with high productivity and at low cost.